You want 100% uptime
When I was first learning how to play a rogue, a more experienced assassin shared a tip with me: "The purest way to increase your DPS is to just attack more." While the advice is simple, the truth still rings true today. If you spend 5% of a fight not attacking, you're doing 5% less damage than you could be. Not attacking something is literally the worst thing you can do. You can forget Slice and Dice and your other finishers, and you'll still do more DPS if you stay on the target full-time. If you're looking to maximizing your performance, maximizing your melee range uptime is the first thing you want to focus on.
While tools like Recount and World of Logs can report your estimated uptime, they only paint part of the picture. I like to use the Atramedes encounter as an example of how to properly handle a moving boss. I have seen so many rogues simply wait for the tank to bring Atramedes to them. We move faster in Stealth than we do out of it, so we should always be Stealthed behind a boss, ready to unleash our fury. The moment that the tank has aggro, we should be unloading -- Tricks of the Trade handles any threat issues. We lose so much damage for every second we're trying to get in position. Following that up, we shouldn't stop attacking Atramedes until he's out of range. You can stand under him and jump as he's taking off for his air phase, gaining several seconds of extra DPS for being diligent.
Uptime is even more important on shorter encounters, as each second lost is a larger fraction of your overall DPS. Losing even a few seconds of uptime on a dungeon trash pull can drop your damage by many thousands. To use a military reference, you should always be taking point. As I mentioned before, we move incredibly fast while Stealthed. We should be in front of the group, ready to pounce on our enemies at a moment's notice. If we're hanging out behind the healers, it will take us forever to get into position. Rogues should be the first ones in and the last ones out, as we're trying to squeeze every ounce of damage out of each encounter.
Ranged classes have it easy
If we're caught out of position, we should use Sprint or Shadowstep to get back into melee range. Every time we move, it should be to maximize our uptime. We need to learn how to tiptoe along the edge of a slime puddle to stay on target. We need to remember where adds spawn so that we can be there to greet them. As a rule of thumb, if you're not stabbing something at all times, you're probably doing something wrong. Obviously there are times when we can't attack, but they should be the exception to the rule. While hunters and warlocks can shoot bosses from afar, we have to constantly worry about our positioning.
While uptime is important, we also have to worry about our relative positioning as well. Subtlety rogues simply can't function without being behind the boss, while assassination rogues will see their DPS plummet when attacking from the front. Combat rogues have it slightly better here, due to their high expertise and lack of position-specific abilities, but there's still a dire cost to standing in front a mob. There are cleave attacks and fire breaths to worry about, and it's always a DPS loss. We have to worry about always being in range and always being in the right position. We have no choice but to adapt by rising to the challenge, as otherwise, we'll fall even further behind on movement-intensive fights.
Know when to cheat
Let me dispel a common misconception: You don't need to use your full rotation on every enemy you encounter. In a dungeon run, there are plenty of situations where you want to just spam Fan of Knives. I get a lot of emails from frustrated rogues who feel like they're doing poorly in heroic dungeons. The issue is usually that they're trying to set up a slow rotation on every mob instead of popping Blade Flurry or spamming Fan of Knives. The other DPSers in your group are dropping their Blizzards and their Whirlwinds, and you won't be able to keep up if you're trying to whittle down one mob at a time. Fan of Knives is on your bar for a reason, and you need to know when to use it.
Similarly, I see a lot of rogues try to use their full rotation on heroic dungeon bosses. Most of the high-end rotation discussions are based around raid encounters where bosses stay alive long enough for abilities like Rupture to do their full damage. We still want to keep Slice and Dice active, but moves like Rupture are often wasted on mobs that are going to die soon anyway. You are competing with the other DPS in your group for every point of health that a mob has. If you don't get to it first, someone else will. Even if you put up a ton of DOTs on a mob, your DPS will be awful if someone else kills it before your bleeds have the time to slowly tick. Rogues aren't the best class for burst DPS due to mechanics like Deadly Poison stacking and Bandit's Guile, but we do the best we can and we try to make up for it in other ways.
Comparing yourself to others
Rogues aren't the best DPS class in the game. As much as I'd like for us to top the charts, the numbers and the encounters simply aren't in our favor. For every amazing rogue out there, there's an amazing hunter who will simply blow him away on the DPS meters. We should still be trying our hardest and pushing our rogues as far as we can, but there's nothing wrong with being beat. Your goal should be to be the best rogue that you can be and hope that Blizzard sorts out the rest. You should be especially cognizant of the differences between the classes when looking at performance in a dungeon environment. There are classes with tons of burst DPS that can simply unleash a tremendous amount of damage in a very short time, which makes them ideal for the bursty playstyle of heroics and dungeons.
Just because the spreadsheets or Shadowcraft says you should be doing 20k DPS doesn't mean that you actually do that much. In dungeons, you don't have the time or buffs to rise to that echelon of DPS. In a raid environment, there are plenty of variables that will bring your damage down. You lose DPS for every interrupt you use, every second that you can't attack, and for every mob that you have to switch to. Unless you're attacking a target dummy with a full raid's worth of buffs and debuffs complementing you, you won't reach your spreadsheet DPS. Your job is to get as close to that number as possible, but don't think you're a failure for not reaching it. It's your job to make the right choices and to do all the damage that you can do, because there's nothing more you can do.
Check back every Wednesday for the latest rogue strategies, from rogue basics and kicking your interrupts into high gear to how to handle your dual-spec rogue and how to pickpocket top tips from top-performing rogues.